Solvent bonding of fiber fleeces including shock-like heat treatment prior to complete vaporization of solvent



United States Patent 3,403,969 SOLVENT BONDING 0F FIBER FLEECES INCLUD- ING SHOCK-LIKE HEAT TREATMENT PRIOR TO COMPLETE VAPORIZATION OF SOLVENT Fritz Kautny, Post Pernitz, Lower Austria, and Rudolf Hemersan, Vienna, Austria, assignors to Firma Bunzl & Biach Aktiengcsellschaft, Vienna, Austria, a corporation of Austria No Drawing. Filed Oct. 22, 1963, Ser. No. 318,098 Claims priority, application Austria, Oct. 29, 1962, A 8,523/62 11 Claims. (Cl. 8130.1)

The present invention relates to a method of solidifying of fiber fleeces.

In the production of fleece fabrics which are also called nonwoven fabrics, it is already known to solidify these fabrics by different measures. Prefabricated loose fiber fleeces, which may consist of different kinds of fibers, are treated thereby with suitable binding agents, By these binding agents it is brought about, that the individual fibers of the fleece fabric are connected together at their respective engagement points, whereby the entire fleece fabric is solidified.

Aside from the application of binding agents for the solidification of fiber fleeces, it is also known already to subject the individual fibers in the fleece first to swelling, whereby the swelled fibers can be connected together again at the engagement points. In these so-called swelling treatments, the swelling means must be removed against thereafter from the fibers. This swelling procedure has been practically confined to cellulose-like fibers until now. The swelling procedure can there never be separated completely from the actual dissolving procedure, whereby a particularly exact procedural technique is required, which moves within very narrow ranges. As swelling means alkaline agents are frequently used as wetting agents, which lead to a fast depolymerization of the cellulose molecules. As such means may be mentioned by example: caustic soda, calcium rhodanide, zinc chloride, tetrammine-cupro-hydroxide known under the trademark Cuoxam and other metal-ammonia-complexes, known under the trademark Jaime complex-salts, whereby the latter are preferred, since they lead only to slight depolymerization of the cellulose molecules. The swelling means must be neutralized and Washed out, respectively, from the fleece fabric.

All the processes known heretofore for the solidification of the fiber fleeces are characterized by more or less strong drawbacks. For instance, by the application of binding means, the original characteristics of the fibers, such as, for example, elasticity, grip, volume, etc., are more or less strongly changed. By the application of the heretofore known swelling agents, frequently a depolymerization of the fibers takes place, the connection between the individual fibers is often not satisfactory and due to the decomposition of the individual fiber molecules, the chemical resistance of the fiber is also affected disadvantageously.

It is, therefore, one object of the present invention to provide a method of solidifying of fiber fleeces, wherein these drawbacks are to be avoided.

It is another object of the present invention to provide a method of solidifying of fiber fleeces, wherein surprisingly the individual fibers can be connected together, without taking in stride these drawbacks, by the treatment of these fiber fleeces with a volatile solvent, which swells and dissolves, respectively, the fiber not at all and slightly only, respectively, in its cold state, and appreciably stronger in its warm state, whereupon the such treated fiber fleece is subjected to a short, shock-like heat treatment and, finally, the used solvent is completely removed Patented Oct. 1, 1968 from the fiber fleece by vaporization. The solvent can be converted into vapor either naturally without application of heat under normal atmospheric pressure at room temperature or artificially by the application of heat or lower pressure. As volatile swelling and solving agents, respectively, in accordance with the definition given above, also mixtures of individual components can be used.

It is yet another object of the present invention to provide a method of solidifying of fiber fleeces, wherein the application of the mixture of swelling and solving agents, respectively, can be performed, for example, by spraying the agent into the fleece, preferably, from both sides of the fleece either simultaneously or successively. Suitably about 30 to g./m. are sprayed into the fleece.

It is still another object of the present invention to provide a method of solidifying of fiber fleeces, wherein at first a mixture of the solventand the swelling-agent, respectively, with air, i.e., a foam, is applied to the fleece, for example, by means of rollers arranged on both sides of the fleece, whereby about 6 to 8 times of the solvent mixture can be applied, then it is possible by the spraying method. In this case it is suitable to add a small quantity of surface active materials to the solventand swellingagent, respectively. Furthermore, during the feeding of the solvingand swelling-agent, respectively, to be used in accordance with the present invention, in addition other materials, such as hydrophobic agents, which are to be present later on in the fleece in certain types of fleeces, can also be fed thereto, provided that they do not have any disturbing effect in the following method types, i.e., for example, that they evaporate or decompose during the shock-like heat treatment. Furthelmore, it is possible to support the feeding of the solvent and swelling agent, respectively, of the present invention into the fiber fleece, in particular during the spraying, such that the opposite side of the fleece is subjected to vacuum.

It is yet another object of the present invention to provide a method of solidifying of fiber fleeces, wherein the shock-like heat treatment is brought about by means of infrared ray applications or by application of a high frequency field.

The fiber fleeces manufactured in accordance with the present invention have maximum porosity and complete preservation of their volume, and the natural fiber grip is retained to the greatest extent; the fleeces are resistant against all agents which do not attack the fibers themselves and can, therefore, upon proper selection of the fibers be chemically cleaned, washed and form-retained.

This method is applicable in principle to all types of fibers, suitable for the manufacture of fiber fleeces and for which solvents exist which correspond with the above mentioned criteria. There are particularly those which are, preferably, used as spinning solvents. The method according to the present invention has been shown particularly advantageous for the manufacture of solidified fiber fleeces containing acrylic fibers, particularly polyacrylonitrile fibers, so that the method will be further explained below in relation with ths type of fibers.

As a solvent for the manufacture of solidified fiber fleeces with a content of polyacrylonitrile, in particular dimethyl sulfoxide, can be used. In its pure form DMSO has several shortcomings. 'It is, for example, strongly hygroscopic and furthermore very inflammable; moreover its solution capacity for polyacrylonitrile fibers is so strong in its pure state, that a fiber deformation takes place upon performance of the method according to the present invention.

In order to meet these shortcomings, it has been established, at first that DMSO is to be used suitably in mixtures with water. A mixture of about 30 parts DMSO and 70 parts water has a solving capacity for polyacrylonitrile fibers corresponding with the above mentioned criteria and, furthermore, it is no more hygroscopic, so that it can be stored also in open containers for any chosen time period, without, thereby, changing the concentration of the mixture.

To meet the danger of fire, it has been found proper to perform the short shock-like heat treatment, provided in accordance with the present invention, for the fiber fleece treated with the mixture of DMSO and water, in an atmosphere of an inert gas. This atmosphere of inert gases can be obtained either by blowing an inert gas, as for example, carbondioxide, nitrogen or the like, into the heating chamber, or a liquid,non-combustible solvent can be admixed to the DMSO-water-mixture, which solvent evaporates in the heating chamber and provides there the atmosphere of inert gases. As such solvents, in particular methylene chloride has been found useful. A mixture of about 30 parts DMSO, 70 parts Water and 10 parts methylene chloride has no more the danger of fire under the given conditions of procedure and moreover, is also better suitable in its other characteristics for the method of the present invention. In the production of this mixture, attention has to be paid, that the methylene chloride is at first admixed to the pure DMSO, whereafter the methylene-chloride-DMSO-mixture is added to the water under stirring and strong cooling, since otherwise a homogeneous mixture and solution, respectively, of the three components almost cannot be obtained.

EXAMPLE 1 A fiber fleece consisting of 100 parts by weight of polyacrylonitrile of 6 denier, 60 mm. staple having a weight of 80 g./m. is at first sprayed from one side with a mixture of 30 parts by weight of DMSO, 70 parts water and 10 parts methylene chloride. Immediately upon applying the mixture, the fiber =fleece is fed into a heating zone, in which it is heated within the shortest possible time to a temperature of about 200 C. during a time period of about 10 seconds. After emerging from the heating zone the fleece is dried under moderate heat of about 120 C. under air circulation. Thereafter, the other side of the fleece is treated in the same manner (spraying, heat shock, drying). A fiber fleece is obtained, which is completely scentless and free from foreign binding agents and which has an extraordinary inner solidification.

EXAMPLE 2 A fiber fleece consisting of 60% polyacrylonitrile of 6 denier, 60 mm. staple, 20% polyamide of 4 denier, 500 mm. staple and 20% polyester fiber of 3 denier, 40 mm. staple, manufactured by the Randow-weaving process, is rendered into a foamy state and pressed into the fiber fleece with a mixture of 30 parts by weight of DMSO, 70 parts of water, 10 parts of methylene chloride and 3 parts tertiary octlyphenoxy polyoxyethanol with about 35 oxyethylene units. Immediately after applying the air containing mixture, the latter is subjected to a heat shock of about 180 to 220 C. for a short time period and, thereafter, the fleece is dried at about 120 C.

While we have disclosed several embodiments of the present invention, it is to be understood that these embodiments are given by example only and not in a limiting sense, the scope of the present invention being determined by the objects and the claims.

4 We claim: 1. A method of solidifying of acryl fiber fleeces, particularly polyacrylonitrile comprising the steps of:

treating an acryl fiber fleece with at least a single solvent mixture capable of swelling and dissolving, respectively, at least a part of the fibers of said fleece,

subjecting said treated fiber fleece to a short intensive shock-like heat treatment,

removing said mixture from said fleece by vaporization,

and

said solvent mixture comprises dimethyl sulfoxide as a solving component and water.

2. The method, as set forth in claim 1, wherein:

said acrylic fibers comprise polyacrylonitrile fibers.

3. The method, as set forth in claim 1, wherein:

said step of treating said fiber fleece is performed by spraying said solvent mixture into said fiber fleece to at least one side thereof.

4. The method, as set forth in claim 1, wherein:

said step of treating said fiber fleece is performed by pressing said solvent mixture in a foamy state into said fiber fleece.

5. The method, as set forth in claim 1, wherein:

said step of subjecting said fleece to a short shock-like heat treatment is performed by applying infrared radiation to said fleece.

6. The method, as set forth in claim 1, wherein:

said step of subjecting said fleece to a short shock-like heat treatment is performed by applying a high frequency field to said fleece.

7. The method, as set forth in claim 1, wherein:

said step of subjecting said fleece to a short shock-like heat treatment is performed in an atomsphere of an inert gas.

8. The method, as set forth in claim 7, wherein:

said inert gas comprises the vapor of a noncombustible solvent having a low boiling point.

9. The method, as set forth in claim 1, wherein:

said solvent mixture further includes methylene chloride.

10. The method, as set forth in claim 9, wherein:

said step of treating said fiber fleece is performed by spraying said solvent mixture and the latter comprising about 30 parts dimethyl sulfoxide, parts water and 10 parts methylene chloride.

11. The method, as set forth in claim 9, wherein:

said solvent mixture is prepared by first mixing said dimethyl sulfoxide with said methylene chloride and then adding water, and then stirring and cooling.

References Cited UNITED STATES PATENTS 2,590,850 4/ 1952 Dungler 8-149.3 2,914,422 11/1959 Pratt et al 8130.1 X 3,053,609 9/1962 Miller 8130.1 X 3,143,437 8/1964 Rosset 8 -130.1 X 3,236,587 2/1966 Genereux 8-1301 NORMAN G. TORCHIN, Primary Examiner.

I. C. CANNON, Assistant Examiner. 

1. A METHOD OF SOLIDIFYING OF ACRYL FIBER FLEECES, PARTICULARLY POLYACRYLONITRILE COMPRISING THE STEPS OF: TREATING AN ACRYL FIBER FLEECE WITH AT LEAST A SINGLE SOLVENT MIXTURE CAPABLE OF SWELLING AND DISSOLVING, RESPECTIVELY, AT LEAST A PART OF THE FIBERS OF SAID FLEECE, SUBJECTING SAID TREATED FIBER FLEECE TO A SHORT INTENSIVE SHOCK-LIKE HEAT TREATMENT, REMOVING SAID MIXTURE FROM SAID FLEECE BY VAPORIZATION, AND SAID SOLVENT MIXTURE COMPRISES DIMETHYL SULFOXIDE AS A SOLVING COMPONENT AND WATER. 